Cam chain tensioner lock nut

[junkshow]

Just wondering if some year XS650's don't use a lock nut on the cam chain tensioner. Mine doesn't have one an it doesn't even look like one would fit.

My engine is a '76 I believe (S/N: 2FO-113xxx).

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[5twins]

Yes, Yamaha eliminated the lock nut for several years during the production run, from '76 to '78 I believe. They then brought it back. That should tell you something, like having one is a good idea. You can add one from the later engines if you use the later plunger too (its longer than yours). In order to provide enough space on the adjuster screw for both the lock nut and the acorn cap, it has to be backed out more from the housing. To achieve proper chain tension with it backed out more, you need a longer plunger.

 

[Brian902]

5Twins has a good picture here in post #4

http://www.xs650.com/forum/showthread.php?t=27334&highlight=cam+chain+tensioner

 

[junkshow]

Thanks 5Twins and Brain902,

This place has been a wealth knowledge that without guys like you and this forum, I would still be staring an a box of XS parts.

Now I'm off to search for a new longer plunger.

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[5twins]

You'll need the later lock nut as well. If you look at the lock nuts in the link above, you'll notice the early ones are just a plain looking nut. The later style has a collar on it. You need that because the surface it tightens against on the housing is inset or counter-bored into the housing a little. A plain nut won't fit in there.

 

[xjwmx]

The lock nut is hard to get a wrench on, being thin and and sort of back in there. Next time you have it loose take it off and see if a wrench has rolled up any metal onto the face of the nut. You can use a flat file to remove it. It can keep the acorn from fitting right and cause a small leak or tear up the o-ring. A deep thin walled 27mm socket would avoid that.

 

[Grinder]

I often wondered on my 77 if I could just back the threaded rod out and clean it off with carb cleaner or similar and put a dab of blue loctite on the shaft where it needs to be to hold the adjustment better.